Rotation shaft, feeding device, motor and manufacturing method for rotation shaft

ABSTRACT

A rotation shaft includes a spiral groove for feeding which is formed on the outer peripheral face of the rotation shaft and a plurality of fine recessed parts which is formed on a flank surface of the spiral groove. The rotation shaft may be manufactured by a spiral groove forming step which forms a spiral groove on an outer peripheral face of the rotation shaft and a roughening step which forms a plurality of fine recessed parts on the flank surface of the spiral groove by using a first abrasive medium whose size is set to be capable of reaching to the flank surface. The rotation shaft may be preferably applied to a feeding device and a motor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Application No. 2004-335950 filed Nov. 19, 2004, which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a rotation shaft where a spiral groove is formed on its outer peripheral face, a feeding device and a motor provided with the rotation shaft and a manufacturing method for the rotation shaft.

BACKGROUND OF THE INVENTION

In an optical disk reproduction/recording device which performs reproduction or recording information from or on an optical recording disk such as a CD, an optical head device on which an objective lens and various optical elements are mounted is moved by using a feeding device in a radial direction of the optical recording disk. A stepping motor which is provided with a rotation output shaft where a spiral groove is formed on its outer peripheral face is used in the feeding device. A rack part provided in the optical head device is engaged with the spiral groove of the rotation output shaft to linearly drive the optical head device along the axial direction of the rotation output shaft.

The spiral groove of the rotation output shaft is formed by mechanical working such as rolling, cutting, grinding or the like, and the flank surface is formed in a substantially smooth surface (see, for example, Japanese Patent Laid-Open No. Hei 8-340668).

In the feeding device constructed as described above, lubricant such as grease or oil is coated in the spiral groove to reduce friction between the rack part and the spiral groove and thus wear of the rack part and the spiral groove is prevented. However, since the flank surface of a conventional spiral groove is commonly formed in a mirror surface, it is difficult for the lubricant to be held and retained on the spiral groove. Therefore, in the conventional feeding device, when feeding operation is repeatedly performed, grease shortage occurs on the flank surface of the spiral groove. In the case that the rotation output shaft is formed of brass, when lubricant shortage described above occurs, the lubricant discolors black due to wear powder and the appearance of the rotation output shaft is significantly deteriorated. In addition, when the rack part is formed of resin, the rack part wears easily causing hindrance in the feeding operation. Further, when wear occurs as described above, noise is generated between the rack part and the spiral groove of the rotation output shaft to give a discomfort feeling to a user.

SUMMARY OF THE INVENTION

In view of the problems described above, it is an object and advantage of the present invention to provide a rotation shaft which is capable of preventing wear by enhancing holding power of lubricant on a spiral groove for feeding, and a feeding device, a motor and a manufacturing method for the rotation shaft.

In order to achieve the above object and advantage, according to an embodiment of the present invention, there is provided a rotation shaft including a spiral groove for feeding which is formed on an outer peripheral face of the rotation shaft, and a plurality of fine recessed parts which is formed on a flank surface in the spiral groove.

In accordance with an embodiment of the present invention, the flank surface of a spiral groove formed on the outer peripheral face of a rotation shaft which is used in a feeding device is formed with a plurality of fine recessed parts in a dispersed state. Therefore, when lubricant such as grease or oil is coated on the spiral groove, a high degree of holding power of the lubricant on the spiral groove can be attained. Further, when a feeding device is constructed in which the rack part of a movable body is engaged with the spiral groove of the rotation shaft, the lubricant is held on the spiral groove all the time even when feed operations are performed repeatedly. Accordingly, even when the rotation output shaft is formed of brass, the situation can be prevented in which the lubricant discolors black due to wear powder to cause the appearance of the rotation output shaft to deteriorate. Further, even when the rack part is formed of resin, since wear of the rack part can be prevented, the feeding operation can be stably performed over a long time period. In addition, the occurrence of noise between the rack part and the spiral groove of the rotation output shaft can be prevented.

This invention is effectively applied to a rotation shaft whose raw material is nonferrous metal such as copper alloy or aluminum. In other words, when shortage of lubricant occurs in the case that raw material of the rotation shaft is nonferrous metal such as copper alloy or aluminum, the lubricant is easy to discolor black due to wear powder. However, according to an embodiment of the present invention, this problem can be effectively prevented.

According to an embodiment of the present invention, there is provided a feeding device including a rotation shaft which is formed with a spiral groove for feeding on an outer peripheral face of the rotation shaft and the spiral groove of the rotation shaft is provided with a plurality of fine recessed parts which is formed on a flank surface of the spiral groove. The feeding device also includes a rack part which engages with the rotation shaft, a movable body which is linearly driven in an axial direction by rotation around the axial line of the rotation shaft, and lubricant which is coated on the spiral groove of the rotation shaft.

This invention is effectively applied to a feeding device which is provided with a rack part made of resin. In other words, when shortage of lubricant occurs in the case that the rack part is made of resin, the rack part is easy to be worn to cause a problem to occur in feeding operations. However, according to an embodiment of the present invention, this problem can be effectively prevented.

The rotation shaft in accordance with an embodiment of the present invention can be used as the rotation output shaft of a motor. In this case, the motor includes a main motor body in which the rotation output shaft is rotated around its axial line.

According to an embodiment of the present invention, there is provided a manufacturing method for a rotation shaft including a spiral groove forming step which forms a spiral groove on the outer peripheral face of the rotation shaft, and a roughening step which forms a plurality of fine recessed parts on the flank surface of the spiral groove by using a first abrasive medium whose size is set to be capable of reaching to the flank surface. According to an embodiment of the present invention, a plurality of fine recessed parts can be easily formed on the flank surface of the spiral groove formed on the outer peripheral face of the rotation shaft and a large quantity of rotation shafts can be efficiently processed.

This invention is effectively applied to a rotation shaft whose raw material is nonferrous metal.

In accordance with an embodiment of the present invention, it is preferable that the roughening step uses mixed media of the first abrasive medium and a second abrasive medium whose size is larger than the size of the first abrasive medium. According to the manufacturing method for the rotation shaft described above, roughening of the flank surface of the spiral groove and deburring can be simultaneously performed and thus productivity of the rotation shaft can be improved.

In accordance with an embodiment of the present invention, roughening step and deburring step, which removes burr from the rotation shaft by using a second abrasive medium whose size is larger than the size of the first abrasive medium, may be performed separately.

Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings that illustrate, by way of example, various features of embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a schematic plan view showing an optical disk reproduction/recording device in which a feeding device in accordance with an embodiment of the present invention is provided and FIG. 1(b) is a side view showing the essential portion of the feeding device.

FIG. 2(a) is an enlarged side view showing a rotation shaft in accordance with an embodiment of the present invention and FIG. 2(b) is an enlarged cross-sectional view showing a spiral groove.

FIG. 3 is an explanatory view showing the flank surface of a spiral groove provided on a rotation shaft in accordance with an embodiment of the present invention which is observed with an electron microscope when the flank surface is magnified to 1000 times.

FIGS. 4(a) and 4(b) are graphs showing a cross-sectional curve and a roughness curve of the flank surface before barrel processing is performed on the flank surface.

FIGS. 5(a) and 5(b) are graphs showing a cross-sectional curve and a roughness curve of the flank surface after barrel processing has performed on the flank surface by using media for barrel of round balls (made of ceramic).

FIGS. 6(a) and 6(b) are graphs showing a cross-sectional curve and a roughness curve of the flank surface after barrel processing has performed on the flank surface by using media for barrel in various shapes whose surface is rough (made of ceramic).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1(a) is a schematic plan view showing an optical disk reproduction/recording device provided with a feeding device to which the present invention is applied and FIG. 1(b) is a side view showing an essential portion of the feeding device. FIG. 2(a) is an enlarged side view showing a rotation shaft in accordance with an embodiment of the present invention and FIG. 2(b) is an enlarged cross-sectional view showing a spiral groove. FIG. 3 is an explanatory view showing the flank surface of a spiral groove provided on a rotation shaft to which the present invention is applied, which is observed with an electron microscope when the flank surface is magnified to 1000 times.

An optical disk reproduction/recording device 1 shown in FIG. 1(a) is a device for performing reproduction or recording information from or on an optical recording disk such as a CD or a DVD. The optical disk reproduction/recording device 1 includes an optical head device 2 (movable body) on which various optical elements such as an objective lens 6 are mounted, a feeding device 10 for moving the optical head device 2 in a radial direction of the optical recording disk, a disk drive device 3 which is provided with a spindle motor 7 for rotationally driving the optical recording disk, and a device frame 4 on which the feeding device 10, the disk drive device 3 and the like are mounted.

The feeding device 10 is provided with a first guide shaft 11 and a second guide shaft 12 which are extended parallel toward the radial direction of the optical recording disk on both sides of the optical head device 2. Respective both ends of the guide shafts 11, 12 are fixed to the device frame 4. Further, the optical head device 2 is provided with a bearing part 201 engaging with the first guide shaft 11 at one of both end portions of the optical head device 2 and a pair of bearing parts 202, 203 engaging with the second guide shaft 12 at the other of both end portions of the optical head device 2.

As shown in FIG. 1(b), the feeding device 10 includes a PM type of stepping motor 20 from which a rotation output shaft 22 is extended so as to be parallel to the first guide shaft 11 and the second guide shaft 12. In the stepping motor 20, the base end side of the rotation output shaft 22 is coupled to a main motor body 26 in which a stator and a rotor magnet for rotating the rotation output shaft 22 around its axial line is provided in a motor case 27. Further, a frame 21 in a U-shaped cross-section is fixed on an end face of the motor case 27 where the rotation output shaft 22 is extended in the stepping motor 20. The tip end of the rotation output shaft 22 is rotatably supported by a bearing 215 which is fixed to a rising part 211 of the tip end part of the frame 21.

In the feeding device 10 in accordance with an embodiment of the present invention, the rotation output shaft 22 of the stepping motor 20 is constructed such that a spiral groove 23 is formed on the outer peripheral face of a shaft body whose raw material is made of nonferrous metal such as copper alloy. In the optical head device 2, a rack part 30 is formed as a connecting part with the rotation output shaft 22. In accordance with an embodiment of the present invention, the spiral groove 23 is formed as a double threaded screw. The rack part 30 is formed of a resin plate which is provided with two branched tip end parts 35, 36. A first projection 31 and a second projection 32 which are fitted to the spiral groove 23 of the rotation output shaft 22 are respectively formed in the two tip end parts 35, 36 as shown in FIG. 2(a). The resin plate constructing the rack part 30 is elastically deformed in the state that the projections 31, 32 at the tip end parts of the rack part 30 are fitted to the spiral groove 23. Therefore, the rack part 30 is urged in a direction such that the projections 31, 32 at the tip end parts 35, 36 are entered into the spiral groove 23 deeply. Accordingly, when electric power is supplied to the stepping motor 20 in the feeding device 10, the rotation output shaft 22 is rotated around the axial line and the rotating force is transmitted to the optical head device 2 through the spiral groove 23 and the rack part 30. As a result, the optical head device 2 moves back and forth linearly toward the radial direction of an optical recording disk in the direction of the arrows “A” and “B” while it is guided by the first guide shaft 11 and the second guide shaft 12 (see FIGS. 1(a) and 1(b)). Lubricant such as grease 40 is coated on the spiral groove 23 of the rotation output shaft 22 to reduce a frictional force between the spiral groove 23 and the projections 31, 32 of the rack part 30.

In the feeding device 10 constructed as described above, in accordance with an embodiment of the present invention, a surface roughing processing is performed on the spiral groove 23 of the rotation output shaft 22 of the stepping motor 20, and thus a plurality of, concretely, a number of fine recessed parts 25 is formed on the flank surface 24 of the spiral groove 23 in a dispersed state as described below in detail.

The recessed parts 25 are shown in FIG. 3, formed as a hole with a diameter from 1 μm to several μm, or a groove with a width from 1 μm to several μm. The fine recessed parts 25 are formed by barrel processing described below and thus they may be also formed on a portion other than the spiral groove 23 of the rotation output shaft 22.

In the feeding device 10 and the stepping motor 20 constructed as described above, a plurality of, concretely, a number of fine recessed parts 25 are formed on the flank surface 24 in a dispersed state and thus the spiral groove 23 with a high degree of holding power to the grease 40 can be obtained. Therefore, even when a feeding operation of the optical head device 2 is repeatedly performed by the feeding device 10, the grease 40 is held in the spiral groove 23 all the time. Accordingly, frictional force occurred between the spiral groove 23 and the rack part 30 can be kept small all the time. Consequently, even when the rotation output shaft 22 is formed of a relatively soft nonferrous metal such as brass, the rotation output shaft 22 does not wear and thus the lubricant 40 does not discolor black based on wear powders. Further, even when the rack part 30 is formed of resin, wear of the rack part 30 can be prevented and thus feeding operation can be stably performed over a long period. In addition, the occurrence of noise between the rack part and the spiral groove of the rotation output shaft can be prevented.

FIGS. 4(a) and 4(b) are graphs showing a cross-sectional curve and a roughness curve of the flank surface before barrel processing is performed on the flank surface. FIGS. 5(a) and 5(b) are graphs showing a cross-sectional curve and a roughness curve of the flank surface after barrel processing has performed on the flank surface by using media for barrel of round balls (made of ceramic). FIGS. 6(a) and 6(b) are graphs showing a cross-sectional curve and a roughness curve of the flank surface after barrel processing has performed on the flank surface by using media for barrel in various shapes whose surface is rough (made of ceramic).

In the case that the rotation output shaft 22 in accordance with an embodiment of the present invention is produced which is used in the feeding device 10 and the stepping motor 20, first, the spiral groove 23 is formed to a shaft body made of copper alloy such as brass by applying mechanical working such as rolling, cutting and grinding (spiral groove forming step).

In the spiral groove forming step, in the case of a so-called round form-rolling working, the shaft body is disposed between a pair of rolled thread rolling dies, which is comprised of a fixed die and a movable die rotating in the same direction in a thread rolling machine. The movable die is moved in a direction to the fixed die to pinch the shaft body and, in this state, the shaft body is relatively moved in the axial direction with respect to the movable die and the fixed die while rotating the fixed dice, the movable dice and the shaft body. As a result, the outer peripheral face of the shaft body is plastically deformed by the fixed die and the movable die and the rotation output shaft 22 is produced on which the spiral groove 23 provided with a double threaded screw is formed on its outer peripheral face.

Next, barrel processing (abrasion processing) is performed on the rotation shaft by using a first medium for barrel (abrasive medium) with a size which is capable of reaching to the flank surface 24 of the spiral groove 23 of the rotation shaft to form a number of fine recessed parts 25 on the flank surface 24 (roughening process). For example, when the effective diameter of the spiral groove 23 is 0.7 mm or more, the barrel processing is performed on the rotation shaft by using a medium for barrel whose maximum diameter is 0.5±0.2 mm.

For example, when the characteristics of the flank surface 24, which is after rolling working and before barrel processing, were measured by a method which is prescribed in Japanese Industrial Standards (JIS) '94, the following values were obtained.

Ra (arithmetic mean roughness of roughness curve)=0.025 μm.

Rmax (maximum height of cross-sectional curve)=0.478 μm.

Ry (maximum height of roughness curve)=0.188 μm. On the other hand, for example, when barrel processing was performed by a first medium for barrel of a round ball (made of ceramic), the following values were obtained.

Ra (arithmetic mean roughness of roughness curve)=0.055 μm.

Rmax (maximum height of cross-sectional curve)=0.618 μm.

Ry (maximum height of roughness curve)=0.364 μm. Further, when barrel processing was performed by using a first medium for barrel in various shapes whose surface is rough (made of ceramic), the following values were obtained.

Ra (arithmetic mean roughness of roughness curve)=0.067 μm.

Rmax (maximum height of cross-sectional curve)=0.844 μm.

Ry (maximum height of roughness curve)=0.492 μm.

The cross-sectional curve and the roughness curve of the flank surface 24 before performing the barrel processing are shown in FIGS. 4(a) and 4(b). The cross-sectional curve and the roughness curve of the flank surface 24 after the barrel processing has been performed by a first medium for barrel of a round ball (made of ceramic) are shown in FIGS. 5(a) and 5(b). The cross-sectional curve and the roughness curve of the flank surface 24 after the barrel processing has been performed by using a first medium for barrel in various shapes whose surface is rough (made of ceramic) are shown in FIGS. 6(a) and 6(b).

Roughening of the flank surface 24 is effectively performed when the maximum diameter of the medium is smaller than the effective diameter of the spiral groove. However, when the maximum diameter of the medium is too small, it is difficult to perform sufficient roughening to the flank surface 24. Therefore, the conditions such as the size of the medium are preferably set such that the flank surface 24 is formed, for example, in the following levels:

Ra (arithmetic mean roughness of roughness curve)≧0.030 μm;

Rmax (maximum height of cross-sectional curve)≧0.500 μm; and

Ry (maximum height of roughness curve)≧0.200 μm. In addition, the upper limit of the “Ry” is preferably set to be as follows;

Ry (maximum height of roughness curve)≦1.00 μm. This is because when the flank surface 24 becomes too rough, problems such as noise or wear is easy to occur.

In the roughening process, it is preferable to perform the barrel processing by using media which are mixed with the first medium for barrel and a second medium for barrel whose size is larger than the first medium. According to the construction described above, roughening to the flank surface 24 of the spiral groove 23 and deburring can be performed simultaneously and thus productivity of a rotation shaft can be improved. In other words, since the size of the first medium for barrel is small, the effect for performing deburring is small. However, when a second medium for barrel whose size is larger than that of the first medium for barrel is simultaneously used at the time of barrel processing, burr can be efficiently removed by the second medium for barrel. The mixture ratio when both the first medium for barrel and the second medium for barrel are used is, for example, 1:1.

In the barrel processing, a ceramic ball, a steel ball, a copper ball and the like may be used as a medium for barrel, and its processing time is generally from 20 minutes to 30 minutes.

A cleaning step and an inspection step may be performed between respective steps as required. For example, after the step for forming the spiral groove 23 has performed, measurements of the effective diameter of the spiral groove 23 and the like are performed by a three-wire method and the like. The diameter of three wires (three-wire diameter) used in inspection by the three-wire method is shown by the dotted line “L” in FIG. 2(b). In the roughening step, the first medium for barrel is used which has a size to be capable of roughening to an area of the flank surface 24 of the spiral groove 23 nearer to the thread bottom 230 than the position 231 where the diameter of three-wire contacts internally.

In the manufacturing method described above, when the roughening step is performed after the spiral groove forming step, roughening to the flank surface 24 of the spiral groove 23 and deburring are simultaneously performed by using the first medium for barrel with a small size and the second medium for barrel with a large size at the same time. Alternatively, the roughening step with the use of the first medium for barrel with a small size and the deburring step with the use of the second medium for barrel with a size larger than that of the first medium for barrel may be performed separately.

In the embodiment described above, barrel abrasion is used in the roughening step. However, an abrasion method such as abrasive blasting or centerless grinding may be used.

Further, lubricant such as oil may be used in addition to grease.

In addition, in an embodiment of the present invention, the raw material of the rotation output shaft is copper alloy such as brass. However, since wear and wear powder are easy to occur when the raw material of the rotation output shaft is made of nonferrous metal such as aluminum, the application of the present invention is effective to enhance the holding power of grease.

In the embodiment described above, the rotation shaft is used as the rotation output shaft 22 of the stepping motor 20. However, the present invention may be applied to a feeding device 10 in which the rotational drive force of a motor is transmitted through a gear mechanism to a rotation shaft on which the spiral groove 23 is formed on its outer peripheral face. Further, in the embodiment described above, the projections formed in a resin plate are used as the rack part. However, the present invention may be applied to a feeding device in which a screw formed on a nut is used as the rack part.

While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention.

The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. 

1. A rotation shaft comprising: a spiral groove for feeding which is formed on an outer peripheral face of the rotation shaft; and a plurality of fine recessed parts which is formed on a flank surface of the spiral groove.
 2. The rotation shaft according to claim 1, wherein the plurality of fine recessed parts is formed on the flank surface in a dispersed state.
 3. The rotation shaft according to claim 2, wherein the plurality of fine recessed parts is formed on the flank surface by abrasion processing.
 4. The rotation shaft according to claim 3, wherein the plurality of fine recessed parts is formed on the flank surface by using a medium for barrel for the abrasion processing.
 5. The rotation shaft according to claim 1, wherein raw material of the rotation shaft is nonferrous metal.
 6. A feeding device comprising: a rotation shaft which is formed with a spiral groove for feeding on an outer peripheral face of the rotation shaft, the spiral groove of the rotation shaft being provided with a plurality of fine recessed parts which is formed on a flank surface of the spiral groove; a movable body which is provided with a rack part engaging with the rotation shaft and is linearly driven in an axial direction by rotation around an axial line of the rotation shaft; and lubricant which is coated on the spiral groove of the rotation shaft.
 7. The feeding device according to claim 6, wherein the plurality of fine recessed parts formed on the flank surface of the spiral groove of the rotation shaft is formed in a dispersed state.
 8. The feeding device according to claim 7, wherein the plurality of fine recessed parts is formed on the flank surface by abrasion processing.
 9. The feeding device according to claim 8, wherein the plurality of fine recessed parts is formed on the flank surface by using a medium for barrel for the abrasion processing.
 10. The feeding device according to claim 6, wherein raw material of the rotation shaft is nonferrous metal.
 11. The feeding device according to claim 6, wherein the rack part is made of resin.
 12. A motor comprising: a rotation output shaft which is formed with a spiral groove for feeding on an outer peripheral face of the rotation shaft, the spiral groove of the rotation output shaft being provided with a plurality of fine recessed parts which is formed on a flank surface of the spiral groove; and a main motor body which drives the rotation output shaft to rotate around an axial line of the rotation output shaft.
 13. The motor according to claim 12, wherein the plurality of fine recessed parts formed on the flank surface of the spiral groove of the rotation output shaft is formed in a dispersed state.
 14. The motor according to claim 13, wherein the plurality of fine recessed parts is formed on the flank surface by abrasion processing.
 15. The motor according to claim 14, wherein the plurality of fine recessed parts is formed on the flank surface by using a medium for barrel for the abrasion processing.
 16. The motor according to claim 12, wherein raw material of the rotation output shaft is nonferrous metal.
 17. A manufacturing method for a rotation shaft comprising: a spiral groove forming step which forms a spiral groove on an outer peripheral face of the rotation shaft; and a roughening step which forms a plurality of fine recessed parts on a flank surface of the spiral groove by using a first abrasive medium whose size is set to be capable of reaching to the flank surface.
 18. The manufacturing method for a rotation shaft according to claim 17, wherein raw material of the rotation output shaft is nonferrous metal.
 19. The manufacturing method for a rotation shaft according to claim 17, wherein the roughening step uses mixed media of the first abrasive medium and a second abrasive medium whose size is larger than the size of the first abrasive medium.
 20. The manufacturing method for a rotation shaft according to claim 17, further comprising a deburring step which removes burr from the rotation shaft by using a second abrasive medium whose size is larger than the size of the first abrasive medium. 